People show a remarkable ability to learn new concepts. Children learn to classify some animals as dogs, some foods as candy, and some people as relatives, Specialized experts learn to classify some mushrooms as poisonous, some tumors as malignant, and some wines as Bordeauxs. The proposed experiments and model explore how people learn new concepts. The central thesis is that concept learning often changes how objects are organized into features. We may build our concepts from the perceptual features of objects, but the concepts that we build in turn influence what we see as the features. The aim of the proposal is to provide a formal account of the interactions between conceptual and perceptual learning. The first series of experiments explores the mechanisms by which concept learning alters descriptions of the objects to be categorized. Particular emphasis is given to selective attention, unitization (integrating originally separate sources of information), and dimensionalization (isolating originally fused sources of information). The second series of experiments uses established and new operational definitions of features to quantify the influence of concept learning on object organization. A neural network model of concept learning is proposed. In this model, the concepts to be acquired alter the perceptual features used for categorization. Rather than assuming that fixed perceptual features are combined to determine categorization rules, this model allows for a mutual and simultaneous influence between concepts and perception. Medical professionals are often required to learn new concepts (e.g., malignant tumor, eczema, and Parkinson's disease). Many of these concepts have a strongly perceptual basis. An understanding of how perceptual concepts are learned, and how perceptual adaptation supports concept learning, could help to more effectively train medical professionals. More generally, the experimental results provide a framework for understanding expert/novice differences, for applying results on neural plasticity to behavior, for establishing training regimes for improving perceptual abilities, and for refining educational procedures that involve teaching concepts with a strong perceptual component.